Jan Roman Hönnige, PhD student at Cranfield University, will present twice during the 2016 edition of Aeromat, which will be held in Bellevue, Seattle, US between the 23rd and the 25th of May. The two abstracts are as follows:

WAAM uses arc welding processes for the purpose of additive layer manufacturing, i.e. 3D printing. WAAM is finding increasing industrial interest for the fabrication of meter-scale aerospace components. This is primarily due to the significant cost savings and reduced lead times offered by the process. For example, when using WAAM to fabricate aerospace components, buy-to-fly (BTF) ratios of 1.5 are typically achieved, values which are considerably less than those produced via subtractive manufacturing techniques.

The titanium alloy Ti-6Al-4V has received considerable attention with respect to WAAM. This is primarily due to its high cost and usage in the aerospace industry. In the as-deposited state Ti-6Al-4V WAAM components have large, columnar grains which produce anisotropic mechanical properties. The anisotropic properties are often undesirable for production components and are therefore hindering commercialization of Ti-6Al-4V WAAM. Recent research at Cranfield University has overcome this problem via the cold rolling of each deposited layer. The thermal energy provided by the subsequent layer combines with the stored energy of the cold worked grains causing recrystallization. The recrystallization produces a refined, equiaxed microstructure, giving isotropic mechanical properties that are superior to the Ti-6Al-4V parent material. To date, rolling assisted Ti-6Al-4V WAAM has only been investigated for small, linearly-deposited walls. There is a need to develop a multi-directional rolling assisted WAAM machine for the purpose of fabricating meter-scale Ti-6Al-4V aerospace components. Cranfield University is currently addressing this need.

In summary, this presentation reports on the benefits of the WAAM and interpass rolling processes and details Cranfield University’s development of a multi-directional rolling assisted WAAM machine.

WAAM is a high-deposition-rate ALM process that targets the manufacture of large-scale aerospace parts. Compared to conventional subtractive machining, the main benefits of WAAM are the significant time-, material, and cost savings.

Ti-6Al-4V is the material to benefit most from the advantages of WAAM, due to the high material and process costs, therefore making WAAM especially appealing to the aerospace industry. The subsequent deposition of plasma-welded layers causes large residual stresses in the as-deposited near-net-shape state that result in significant distortion of the final part. Furthermore, the microstructure consists of large, columnar grains, which result in anisotropic and inferior mechanical properties when compared to the parent material.

Cranfield University are researching different cold-working strategies to eliminate these undesired phenomena, namely Cold-Rolling, Global Tensioning and Machine Hammer Peening. The aerospace industry has a high interest in vertical cold-rolling, since the key research findings show a significant reduction of residual stresses and distortion. Moreover, interim cold working automatically causes recrystallization of the microstructure, resulting in isotropic and superior mechanical properties. Current investigations aim to find strategies to further improve the great benefits and the ease of implementing cold-working into the production line. Recently a novel Pinch-Rolling tool was developed that was successfully used to build a zero-distortion part with WAAM for the first time.

This presentation reports the potential of cold-working strategies and the recent achievements at Cranfield University, which have significant, practical benefits and may aid industrialisation of the WAAM process for aerospace parts.